The invention relates generally to methods and apparatus for mapping a condition or property of an organ of a subject, and particularly to methods and apparatus for mapping the electrical and/or the mechanical activity of one or more chambers of the heart.
Cardiac arrhythmias, the most common of which is ventricular tachycardia (VT), are a leading cause of death. In a majority of patients, VT originates from a 1 mm to 2 mm lesion located close to the inner surface of the heart chamber. One of the treatments for VT comprises mapping the electrical pathways of the heart to locate the lesion followed by ablation of the active site.
U.S. Pat. No. 5,546,951 and U.S. patent application Ser. No. 08/793,371 and its corresponding application filed under the Patent Cooperation Treaty and published as WO 96/05768, which are incorporated herein in their entirety by reference, disclose methods for sensing an electrical property of the heart tissue, for example, local activation time, as a function of the precise location within the heart. The data are acquired with one or more catheters that are advanced into the heart, the catheters having electrical and location sensors in their distal tips. Methods of creating a map of the electrical activity of the heart based on these data are disclosed in commonly assigned U.S. patent application Ser. No. 09/122,137 filed on Jul. 24, 1998 and in its corresponding published European Patent Application no. EP 974,936, as well as in U.S. patent application Ser. No. 09/357,559 filed on Jul. 22, 1999, the disclosures of which are also incorporated herein in their entirety by reference. As indicated in these applications, location and electrical activity is preferably initially measured at about 10 to about 20 points on the interior surface of the heart. These data points are then generally sufficient to generate a preliminary reconstruction or map of the cardiac surface to a satisfactory quality. The preliminary map may be combined with data taken at additional points in order to generate a more comprehensive map of the heart""s electrical activity. The detailed map so obtained may then serve as the basis for deciding on a therapeutic course of action, for example, tissue ablation, to alter the propagation of the heart""s electrical activity and to restore normal heart rhythm.
Catheters containing position sensors may be used to determine the trajectory of points on the cardiac surface. These trajectories may be used to infer the motion characteristics such as the contractility of the tissue. As disclosed in U.S. Pat. Nos. 5,738,096 and 6,066,094, incorporated herein in depicting such motion characteristics may be constructed when the trajectory information is sampled at a sufficient number of points in the heart. A high quality preliminary map of motion characteristics is dependent on acquiring a sufficient number of points representatively spaced about the heart chamber volume.
In constructing these preliminary maps, it is desirable that the data are sampled at points sufficiently spaced to outline the entire volume of the chamber under study. If the preliminary map adequately outlines the heart volume, acquisition of additional points will generally enable the detailed reconstruction to permit accurate diagnosis and treatment. Occasionally however, incomplete sampling, as, for example, by localizing the sample points to only a portion of the heart volume, will result in the generation of an incomplete map. Further sampling may lead to a more detailed map of the partial cardiac volume, but this may be inadequate for proper diagnosis and treatment.
In creating maps of the heart using the above-referenced systems, the initial data points for the preliminary reconstruction are generally acquired under the guidance of an imaging modality such as fluoroscopy that permits the cardiologist to observe the placement of the catheter tip within the heart chamber. Once the preliminary map is generated, subsequent points may then be acquired under the guidance of the preliminary map and a location system based on, for example, electromagnetic or acoustic sensors. Unfortunately, unassisted fluoroscopy provides relatively poor visualization of topographical features within the heart. While contrast-assisted fluoroscopy, in which a contrast agent is injected into the heart chamber under examination, significantly improves the observation of topography, the contrast agent obscures the observation of the catheter tip. Thus, fluoroscopy is insufficient to properly guide the cardiologist to the points on the interior of the heart necessary for the generation of a preliminary map of the electrical activity that roughly encompasses the complete heart volume. The potentially harmful effects of the contrast agent and of ionizing radiation to the patient also limit the amount of data that can be collected under fluoroscopy.
Electrical activity at a point in the heart is typically measured by advancing a catheter containing an electrical sensor (an electrode) at or near its distal tip to that point in the heart, firmly contacting the tissue with the electrode and acquiring data at that point. Alternatively, electrical activity may be measured with catheters containing multiple electrodes. In the case of catheters with multiple electrodes, one or more electrodes are generally present at the catheter tip and other electrodes may be present along the catheter body.
It is generally important to maintain good electrical contact between the electrodes and the tissue in order to obtain a reliable and stable electrical reading. Fluoroscopy produces images that are lacking in topographical detail. Accordingly, in taking measurements under the guidance of this imaging modality, the catheter tip may not actually be in effective contact with the tissue. Alternatively, it may be possible to bruise the intracardial tissue by excessive pressure of the catheter tip against the tissue while making such measurements.
PCT application WO 98/35720 discloses an x-ray guided surgical location system with extended mapping volume. The application does not teach or suggest navigation of a catheter tip for the purpose of mapping a chamber of a heart guided by topological information contained in acquired images of the chamber.
U.S. Pat. No. 5,391,199 discloses an apparatus and method for treating cardiac arrhythmias. The method of the ""199 patent comprises obtaining a perspective image of the organ to be mapped; advancing one or more catheters to sites adjacent to or within the organ; sensing the location of each of the catheter""s distal tips with a non-ionizing field; sensing local information of the organ; processing the local information to create one or more data points; and superimposing the one or more data points on the perspective image of the organ or structure. The ""199 patent does not teach or suggest the registration of the image with a positional frame of reference of a position sensor contained in or proximate to the catheter tip. Furthermore, the ""199 patent does not teach or suggest navigating the catheter tip under the guidance of topological information contained in acquired images of the chamber.
U.S. Pat. No. 5,433,198 discloses an apparatus and method for cardiac ablation. The apparatus and method of the ""198 patent includes a multi-electrode catheter introduced percutaneously into a subject""s heart and deployable adjacent to various endocardial sites. The electrodes are connectable to a mapping unit, an ablation power unit and a pacing unit, all of which are under computer control. Intracardiac electrogram signals emanated from a tachycardia site of origin are detectable by the electrodes. Their arrival times are processed to generate various visual maps to purportedly provide real-time guidance for steering the catheter to the tachycardia site of origin. In one aspect, the apparatus of the ""198 patent also includes a physical imaging system which is capable of providing different imaged physical views of the catheter and the heart. These physical views are said to be incorporated into the various visual maps to provide a more physical representation. The ""198 patent does not disclose or suggest the use of a catheter having a sensor which provides three-dimensional position information of the catheter tip in a positional frame of reference, nor does it disclose or suggest registering chamber images with said frame of reference.
U.S. Pat. No. 6,052,618 discloses a device for mapping electrical activity in the heart. The device of the ""618 patent has an imaging unit, such as a fluoroscopic imaging unit, for generating a physical in vivo image of a patient""s heart as an anatomical reference image; an electrode catheter with at least one electrode for sensing intracardiac electrical activity in a patient""s heart; and signal processing equipment for determining activation times from sensed electrical activity at different points in the heart. The device of the ""618 patent further includes means for generating a graphic image showing the activation times at different points in the heart and superimposing this graphic image onto the anatomical image. The ""618 patent does not disclose or suggest the use of a catheter having a sensor which provides three-dimensional position information of the catheter tip in a positional frame of reference, nor does it disclose or suggest registering chamber images with said frame of reference. Furthermore, as stated at column 3 lines 34-38 of the ""618 patent, xe2x80x9cIn this type of image, the heart appears, at best, as a pale shadow. The heart is not shown at all in these figures. The body parts seen most clearly in the radiograph are skeletal parts, such as spinal vertebrae and ribs.xe2x80x9d Thus, the ""618 patent does not teach or suggest the use of images containing topological information suitable for guiding the navigation of the catheter tip.
The present invention is directed to a method for intracardially mapping a condition of a chamber of a heart of a subject. The method of the invention is preferably applied to the mapping of an electrical, mechanical or electromechanical condition of the heart chamber. While the method may be applied to any of the heart""s chambers, it is especially useful for the mapping of the left ventricle. The mapping is conducted with a mapping catheter having a distal tip. The catheter distal tip has at least one sensor contained therein or proximate thereto that is capable of sensing condition information of the chamber and providing three-dimensional position information of the catheter tip in a positional frame of reference. The method of the invention involves acquiring a first image of the chamber taken from a first projection and a second image of the chamber taken from a second projection wherein the second projection is different from the first projection. The two projections are preferably separated by an angle of between about 75 degrees to about 105 degrees, and, more preferably, the two projections are separated by an angle of about 90 degrees. The first and second images are taken from two perspectives such as a left anterior oblique (LAO) and a right anterior oblique(RAO) projection. The two images are preferably contrast-assisted fluoroscopic images that depict the chamber at the same phase in the cardiac cycle, preferably, at end-diastole. Both the first and second chamber images contain topological information of the chamber that include the chamber contour. The method further comprises registering the first image and the second image with the positional frame of reference. The distal tip of the mapping catheter is advanced into the chamber to an acquisition point where condition information and position information are to be acquired with the at least one sensor. The catheter tip is navigated to the acquisition point in the chamber guided by topological information contained in or derived from the first and second images. The topological information used to guide the navigation of the catheter is preferably a reconstruction of the chamber, such as a three-dimensional reconstruction derived from the topological information contained in the chamber images. After the condition and position information are acquired at the first acquisition point, the catheter tip is similarly navigated to additional acquisition points where additional condition and position information are acquired. The acquisition points are sufficient in number and spacing throughout the chamber to permit the generation of a map of the condition in the chamber, which is preferably created from the acquired condition and position information.
In one embodiment, the at least one sensor comprises a position sensor capable of providing both three-dimensional position information as well as mechanical condition information. In another embodiment, the at least one sensor comprises a position sensor capable of providing three-dimensional position information and an electrode for sensing electrical information. The at least one sensor preferably comprises an electromagnetic sensor that generates signals responsive to the strength of a magnetic field generated by magnetic field radiators external to the patient wherein the signal intensity is indicative of the three-dimensional position of the sensor in the frame of reference.
The method of mapping a chamber of the heart of the invention further preferably comprises acquiring an image of a scaling object from each of the first and the second projections. The images of the scaling object are used to scale the images of the heart chamber. The method also preferably further comprises affixing a registration position sensor to the patient prior to the acquisition of the first and second images of the chamber. The registration position sensor is affixed to the patient so that an image of the registration position sensor is included in the chamber images. The three-dimensional position coordinates of the registration position sensor are determined and used to register the images of the chamber in the frame of reference.
In another embodiment, the invention is directed to a method for intracardially mapping a condition of a chamber of a heart of a subject. The method of the invention is preferably applied to the mapping of an electrical, mechanical or electromechanical condition of the heart chamber. While the method may be applied to any of the heart""s chambers, it is especially useful for the mapping of the left ventricle. The mapping is conducted with a mapping catheter having a distal tip. The catheter distal tip has at least one sensor contained therein or proximate thereto that is capable of sensing condition information of the chamber and providing three-dimensional position information of the catheter tip in a positional frame of reference. The catheter distal tip is advanced into the chamber and the catheter tip is navigated to an acquisition point in the chamber. Navigation of the catheter tip is guided by a reconstruction, preferably a three-dimensional reconstruction of topological features of the chamber registered in the positional frame of reference. After the condition and position information are acquired at the first acquisition point, the catheter tip is similarly navigated to additional acquisition points where additional condition and position information are acquired. The acquisition points are sufficient in number and spacing throughout the chamber to permit the generation of a map of the condition in the chamber, which is preferably created from the acquired condition and position information.
The reconstruction of the chamber used to guide the navigation of the catheter tip is preferably based on a first image of the chamber taken from a first projection and a second image of the chamber taken from a second projection. The first projection and the second projection are preferably separated by an angle of about 75 degrees to about 105 degrees, and more preferably, by an angle of about 90 degrees. The first image and the second image are preferably taken from an LAO projection and an RAO projection. Each of the first and second images contain topological information of the chamber. The topological information contained in the images preferably comprises the chamber contour. The first and second chamber images are preferably contrast-assisted fluoroscopic images. The images preferably depict the chamber at the same phase of the cardiac cycle, preferably at end-diastole.
In one embodiment, the at least one sensor comprises a position sensor capable of providing both three-dimensional position information as well as mechanical condition information. In another embodiment, the at least one sensor comprises a position sensor capable of providing three-dimensional position information and an electrode for sensing electrical information. The at least one sensor preferably comprises an electromagnetic sensor that generates signals responsive to the strength of a magnetic field generated by magnetic field radiators external to the patient, the signal intensity being indicative of the three-dimensional position of the sensor in the frame of reference.
The method of mapping a chamber of a heart of the invention preferably further comprises acquiring an image of a scaling object from each of the first and second projections. The images of the scaling object are used to scale the chamber images. The method of the invention preferably further comprises affixing a registration position sensor to the patient prior to acquisition of the first and second chamber images. The registration position sensor is affixed to the patient so that an image of the registration position sensor is included in the chamber images. The three-dimensional position coordinates of the registration position sensor are determined and used to register the images of the chamber in the frame of reference.
Another aspect of the invention is directed to an apparatus for intracardially mapping a condition of a chamber of a heart. The apparatus of the invention comprises a mapping catheter having a distal tip. The catheter distal tip has at least one sensor contained therein or proximate thereto. The at least one sensor is capable of sensing condition information of the chamber and provides three-dimensional position information of the catheter tip in a frame of reference. The apparatus of the invention further comprises means for registering a plurality of images of the chamber with the positional frame of reference. The chamber images are taken from a plurality of projections relative to the chamber and contain topological information of the chamber. The apparatus of the invention also comprises signal processing circuits for acquiring condition information and position information at a plurality of acquisition points in the chamber with the at least one sensor wherein the points are sufficient in number and spacing throughout the chamber to permit the generation of a map of the condition in the chamber.
The at least one sensor contained in or proximate to the catheter distal tip preferably comprises a position sensor capable of providing three-dimensional position information and an electrode for sensing electrical information. More preferably, the at least one sensor comprises an electromagnetic sensor that generates signals responsive to the strength of a magnetic field generated by magnetic field radiators external to the patient. The intensity of the signals generated by the sensor is indicative of the three-dimensional position of the sensor in the frame of reference.
The apparatus for mapping a chamber of a heart of the invention preferably further comprises a scaling object. The apparatus also preferably further comprises a registration position sensor to register the images with the frame of reference.
The apparatus of the invention also preferably further comprises image-processing circuits for constructing a reconstruction, preferably a three-dimensional reconstruction of the chamber from topological information contained in the chamber images. The apparatus also preferably further comprises circuits for mapping the condition of the chamber using the condition and position information acquired with the at least one sensor.
In another embodiment, the invention is directed to an apparatus for intracardially mapping a condition of a chamber of a heart of a subject. The apparatus of the invention comprises a mapping catheter having a distal tip. The catheter distal tip has at least one sensor contained therein or proximate thereto. The at least one sensor is capable of sensing condition information of the chamber and provides three-dimensional position information of the catheter tip in a frame of reference. The apparatus further comprises image processing circuits for constructing a topological reconstruction, preferably, a three-dimensional reconstruction, of the chamber in the frame of reference, as well as signal processing circuits for acquiring condition information and position information at a plurality of acquisition points in the chamber with the at least one sensor. Condition and position information is acquired at points sufficient in number and spacing throughout the chamber to permit the generation of a map of the condition in the chamber.
The image processing circuits used in the apparatus of the invention preferably construct the topological reconstruction from a plurality of images of the chamber. The images are taken from a plurality of projections relative to the chamber wherein each image contains topological information of the chamber.
The at least one sensor contained in or proximate to the catheter distal tip preferably comprises a position sensor capable of providing three-dimensional position information and an electrode for sensing electrical information. More preferably, the at least one sensor comprises an electromagnetic sensor that generates signals responsive to the strength of a magnetic field generated by magnetic field radiators external to the patient. The intensity of the signals generated by the electromagnetic sensor is indicative of the three-dimensional position of the sensor in the frame of reference.
The apparatus of the invention preferably further comprises a scaling object. The apparatus also preferably further comprises a registration position sensor to register the images with the frame of reference.
The features and advantages of the invention will be more readily apparent from the detailed description set forth below, taken in conjunction with the accompanying drawings.